Bordallo was married to Ricardo Bordallo, who served as Governor of Guam from 1975 to 1979 and from 1983 to 1987. While serving as first lady, she worked to emphasize the arts in the classroom and to increase awareness of the local Chamorro culture. Bordallo's husband, the former Governor, committed suicide in 1990 when his appeals were unsuccessful and convictions of witness tampering and conspiracy to obstruct justice would require incarceration in federal prison. Bordallo was the first woman Democrat to be elected to the Guam Legislature, and served five terms as a senator from 1981 to 1982 and again from 1986 to 1994. During the 1988 U.S. presidential election, Bordallo was a member of Guam's uncommitted delegation to the 1988 Democratic National Convention.[3]

In 1994, she ran alongside Carl Gutierrez on the Democratic ticket and was elected Lieutenant Governor of Guam, serving from 1995 to 2002, the first woman in Guam's history to hold this position. In this role, she worked to promote tourism, environmentalism, and island beautification.

In 2002, as Bordallo reached her term limit and as Delegate Robert Underwood vacated his seat and attempted to run for governor, she campaigned for and was elected as a Democrat to the House, serving from January 2003 to the present, and is the first woman to represent Guam in Congress. She is one of six non-voting delegates to the House of Representatives. While in Congress, she has devoted herself to economic issues and has helped to pass legislation that aids small businesses on Guam. She has also been involved in military and environmental issues.

In April 2008, Bordallo apologized after an investigative report by the Pacific Daily News revealed that she and Senator Jesse Lujan both claimed to have degrees on their official biographies and resumes when they had not graduated from college.[6]

Bordallo objected to amendments the United States Senate made to the Omnibus Territories Act of 2013. Originally, the bill would have included the provisions to create a fund in the U.S. treasury to pay reparation claims to "living Guam residents who were raped, injured, interned, or subjected to forced labor or marches, or internment resulting from, or incident to, such occupation and subsequent liberation; and (2) survivors of compensable residents who died in war."[7] This provision, however, was removed from the bill. Bordallo was "extremely disappointed" by this change and said that she was "committed to continuing our fight for war claims for our manamko despite all the obstacles the conservative Republicans continue to raise."[8] The changes were made so that the bill could pass by unanimous consent.[8]

In January 2012, Republican Guam Senator Frank Blas Jr. announced he would challenge Bordallo in the upcoming November election for her delegate seat.[9][10] Bordallo defeated Blas in the November general election. She received 19,765 votes (58%) to his 12,995 votes (38%)[11]

In May 2012, Yale graduate and former White House intern Karlo Dizon, Democrat, also announced his bid as delegate to Congress.[12] Bordallo defeated Dizon in the primary election, with 73% of the vote.[13]

By this year 2014 she is running for delegate alongside with Matthew Pascual Artero for the primary election. Bordallo defeated Artero in the primary election on August 30, 2014. In this years election, Republican running candidate Margaret McDonald Metcalfe announced she will challenge Bordallo in the upcoming November election for her delegate seat.